Bacterial involvement in a saddleback disease of the reef silverside, Atherina harringtonensis Goode (Pisces: Atherinidae) from Bermudan waters

Saddle-shaped skin lesions commonly occurring in both wild and captive Bermudan reef silversides yielded a mixed infection of motile and non-motile Gram-negative cells of Acinetobacter calcoaceticus, Pseudomonas sp., Vibrio parahaemolyticus and a myxobacterial-like strain. Host response was minimal, consisting of infiltration of a few lymphocytes and macrophages. The fish pathogenic dinoflagellate Amyloodinium ocellatum was seen in one fish with a saddle lesion and caused muscle cell lysis, as evidenced by cloudy cell swelling. Antibiotic sensitivity tests showed increased drug resistance with mixed bacterial types compared to that of single pure isolates. This suggests that alternatives to chemotherapy for control of bacterial fish diseases is appropriate, because most are probably caused by mixed infections.